The present invention relates to an apparatus for wrapping a band or strip about an object. More particularly this invention concerns an apparatus for securing plastic strapping around a package to be shipped or mailed.
As described in German patent document 100 26 200 of Detleff Scholl et al, a package-strapping apparatus has a housing with a tightening wheel that can be urged against a pair of superposed plastic tapes. A complex system of an overload-cutoff motor, a friction brake, and several one-way clutches cooperate with an eccentric mechanism to allow the wheel to be moved into and out of pinching engagement with the two tapes, and to rotate it in a forward direction that draws them tightly about a package they are looped around, and oppositely to feed in new tape.
This arrangement is quite complex with numerous parts, like the one-way clutches and friction brake, that change operational characteristics with wear so that the device needs frequent attention and adjustment. Furthermore the structure is quite bulky, and in general this strapping apparatus is fairly expensive.
It is therefore an object of the present invention to provide an improved strapping apparatus.
Another object is the provision of such an improved strapping apparatus which overcomes the above-given disadvantages, that is which is of simple, reliable, compact, and inexpensive construction.
A strapping apparatus for securing a tape around a package has according to the invention a housing, a support roll rotatable on the housing, a first clamp on the housing for clamping a free end of the tape to the housing, a second clamp on the housing for clamping the tape offset from its free end to the housing, a cutter on the housing for cutting the tape upstream of the second clamp, and a joiner for securing the tape to itself upstream of the second clamp. A tube shaft is pivotal on the housing adjacent the support roll about a tube-shaft axis, and a drive shaft is rotatable in the tube shaft about a drive-shaft axis parallel to and offset from the tube-shaft axis. A first drive roll on the drive shaft carries a friction layer bearing axially offset from the drive-shaft axis on the housing. Abutments carried by the housing and the tube shaft limit angular movement of the tube shaft about the tube-shaft axis between one end position in which the first drive roll is spaced from the support roll and an opposite end position in which the first drive roll bears via the tape on the support roll. A first drive connected to the drive shaft rotates same and the first drive roll in a clamping direction and thereby oppositely rotates the tube shaft about the tube-shaft axis into the opposite end position and also can rotate the drive shaft and the first drive roll in an opposite freeing direction to thereby oppositely rotate the tube shaft about the tube-shaft axis into the one end position. A controller connected to the first and second clamp, joiner, and first drive synchronizes operation of same.
This structure is extremely compact and simple. The friction layer on the drive roll replaces a complex mechanism employed in the prior art to shift this drive roll into and out of engagement with the support roll. This much simpler mechanism is extremely reliable and has a long service life.
In use the tape passes from a standard supply spool through the strapping apparatus, being spanned over the support roll. A length of the tape at the free end is looped around a package and then inserted into the first clamp by an operator of the machine. The first clamp according to the invention includes a switch connected to the controller and operable by insertion of the free tape end into the first clamp. This switch initially operates the first clamp to lock the free end in place. The controller connected to this switch then operates the drive to rotate the drive shaft in the clamping direction after the switch is operated. Thus poking the free tape end into the first clamp initiates the strapping cycle.
The tube shaft according to the invention carries a tape guide engaging and guiding the tape in the one end position and out of engagement with the tape in the opposite end position. Furthermore, a second drive is provided including a second drive roll engageable with the tape on the support roll and connected to the controller for advancing the tape out of and drawing the tape back into the apparatus. The function of this second drive is to extend enough tape to wrap around the package, and then loosely snug it around the package.
The second drive includes a rocker carrying the second drive roll and pivotal on the housing into and out of a pinching position with the second drive roll pressing the tape against the support roll, and spring biasing mens connected between the rocker and the housing for urging the rocker into the pinching position. Thus this second drive roll constantly presses the tape against the support roll with a generally constant force.
The controller according to the invention includes a start switch operable for initiating rotation of the second drive roll in a direction advancing the tape out of the apparatus. The controller can then automatically stop the second drive roll a predetermined time after operation of the switch so as to extend a predetermined length of the tape.
The second drive includes a reversible electric motor connected to the second drive roll. The switch of the first clamp is connected to the controller so that it can operate the second drive to draw the tape back into the apparatus after the switch is operated. In addition, the controller operates the second drive to draw the tape back into the apparatus a predetermined time after the switch is operated. The switch is a time-delay switch. More particularly the second drive includes a second motor and the controller monitors loading of the second motor and starts the first drive when loading of the second drive motor exceeds a predetermined limit. Thus the first drive, which is the one used to pull the tape very tight around the package, only steps into action when the tape has been snugged loosely around the package by the second drive. In fact the first drive roll does not even engage the tape until the second drive has payed it out and wound it back in.
To achieve this effect the first drive includes a first motor and the controller monitors loading of the first motor and operates the second clamp to clamp the tape when loading of the first drive motor exceeds a predetermined limit. After operating the second clamp to clamp the tape the controller operates the cutter to sever the tape upstream of the second clamp. Similarly, after operating the second clamp means to clamp the tape the controller operates the joiner to secure the tape to itself upstream of the second clamp and downstream of the cutter.
The second drive roll is provided with externally operable hand formations for manual rotation of the second drive roll. Furthermore the first drive includes a motor and a worm-gear transmission connected between the motor and the drive shaft and constructed to be self-blocking. Thus if the first drive stops, the tape will not slide back out and loosen; instead it will be solidly blocked until the first drive is actually reversed to back off the first drive roll.
A spring is braced according to the invention between the friction layer and the first drive roll for pressing the friction layer against the housing. This spring is a stack of Belleville washers.